Cholinergic Urticaria
The condition characterized by urticaria triggered by one's own sweat is called cholinergic urticaria. 1
Classification and Definition
Cholinergic urticaria is classified as a thermal physical urticaria under the broader category of physical urticarias, which are reproducibly induced by specific physical stimuli 1. The British Journal of Dermatology guidelines explicitly list it in their clinical classification table as a distinct subtype of physical urticaria 1.
Key Distinguishing Features
The guidelines note an important nuance: some authorities distinguish cholinergic urticaria from other physical urticarias because it is primarily induced by the stimulus for sweating rather than overheating per se (even though the usual reason for sweating is a raised core temperature) 1.
Clinical Presentation
- Weal duration: The weals of physical urticaria, including cholinergic urticaria, typically resolve within one hour 1
- Trigger: Induced by stimuli that provoke sweating (exercise, hot baths, emotional stress, elevated core body temperature) 2, 3
- Appearance: Small, short-lasting, highly itchy papular wheals that develop simultaneously with sweating 2
Underlying Mechanisms
Research has identified that cholinergic urticaria involves type I hypersensitivity to sweat components in many patients:
- Most patients show immediate-type skin reactions to their own sweat 4, 5
- A major histamine-releasing antigen called MGL_1304 (a 17-kDa protein secreted by Malassezia globosa) has been identified in sweat 6, 7
- Patients have detectable IgE antibodies against MGL_1304 6, 7
- Some patients show impaired sweating linked to reduced expression of acetylcholine receptor M3 (CHRM3) and acetylcholine esterase in sweat glands 8
Subtypes
Recent evidence suggests two subtypes 5:
- Sweat-hypersensitivity type: Strong hypersensitivity to autologous sweat, nonfollicular hives, satellite wheals
- Follicular type: Follicular hives with positive autologous serum skin test, but no sweat hypersensitivity
Important Clinical Pitfall
Reduced or absent sweating is common in cholinergic urticaria patients, especially those with long-standing and severe disease 8. This can be severe and is linked to:
- Long disease duration
- High disease severity
- Reduced sweat gland expression of CHRM3 and acetylcholine esterase 8
Clinicians should specifically assess sweating function when evaluating patients with suspected cholinergic urticaria, as this finding has both diagnostic and prognostic implications 2, 8.